1. Field of the Invention
The present invention relates generally to semiconductor wafer preparation and, more particularly, to a chuck assembly for use in semiconductor substrate spin, rinse, and dry (SRD) modules.
2. Description of the Related Art
Wafer preparation and cleaning operations are performed in the fabrication of semiconductor devices. One common wafer preparation operation dispersedly repeated during substrate preparation is a spin, rinse, and dry operation using a spin, rinse, and dry (SRD) module. Usually, spin, rinse, and dry operations are performed in a process bowl mounted on an SRD housing that is secured to a spindle. Typically, the spindle, a chuck mounted on the spindle, and the wafer held by spindle fingers attached to the chuck are rotated by a motor.
Several limitations are associated with conventional SRD modules. At the outset, the design of conventional SRD chucks is very complex. For instance, the chuck is commonly required to move up and down in the bowl. That is, the chuck typically moves up to receive the wafer, moves down to process the wafer and then up again to hand off the process wafer. In view of this continued movement activity, the chuck must remain properly calibrated so that the chuck comes to rest at the exact process level. Failure to maintain the chuck properly calibrated results in mandatory realignment of the chuck. Of course, the process of realigning the chuck is very time consuming and labor intensive, and requires that the SRD modules be taken off-line for an extended period of time, substantially reducing throughput.
Another limitation associated with conventional SRD chucks is the chuck geometry. The relatively large size and substantial weight of conventional chucks require the use of a significant amount of energy to operate the SRD modules. Additionally, the significantly large size of the chucks requires using larger shafts as well as spindles. Collectively, these limitations mandate using of a larger and more powerful pneumatic control, substantially increasing the cost of the SRD modules as well as the associated operating cost.
The rather large geometry of conventional chucks further hinders the removal and replacement of chucks and spindles for maintenance. For instance, removing and replacing of chucks and spindles are typically very time consuming tasks requiring that the entire chuck and spindle assemblies to be removed, which can take up to several hours. This may have substantial negative effects on the overall throughput of the SRD module, as the SRD module is taken off-line when the chuck assembly or the spindle assembly is maintained.
Still another limitation associated with conventional SRD chucks is fluctuations in air pressure implemented to engage/disengage the process wafer. The air pressure is typically supplied by an air cylinder that drives the shaft, which opens and closes the chuck for engaging/disengaging the process wafer. In conventional SRD modules, air pressure causes the chuck to open, close, or maintain a grip on the wafer during processing. Unfortunately, conventional chucks may not always securely engage the process wafer throughout the spin, rinse, and dry cycle due to fluctuations in supplied air pressure. As a result, the spindle fingers and thus the chuck can potentially lose contact with the wafer edge while the wafer rotates at high RPMs, causing the process wafer to potentially fly off. As can be appreciated, failure to apply consistent and constant air pressure can result in damaged wafers, negatively affecting the overall throughput of an SRD module.
Yet another drawback associated with conventional SRD modules is implementing unbalanced spindle fingers. Typically, the spin, rinse, and dry operations are performed at high RPMs while spindle fingers engage the wafer. Once the spinning operation has concluded, the chuck, the spindle fingers, and the wafer are expected to stop rotating. To the contrary, the engaged wafer sometimes continues to rotate for a split period of time thereafter, damaging the edge of the wafer, thus potentially reducing the overall throughput of the module. Furthermore, in some conventional SRD modules the spindle fingers may sometimes open up during the SRD operation, allowing the wafers to escape the grasp of the spindle fingers. This, of course, will damage the wafers.
Still another challenge faced in using typical SRD chucks and spindles is having chemically incompatible components present within the SRD module. In a typical SRD module, most components are constructed from several different materials. For instance, chucks are usually constructed from stainless steel, while the bowls are made out of polypropylene, and the spindles are made out of stainless steel. As a result, particles or contaminants from chemically incompatible components may enter into chemical reaction with the fluids introduced into the SRD module, recontaminating the SRD module. This recontamination is exacerbated by the chucks having to continuously move up and down (e.g., to load and unload each new wafer) within their respective bowls. For instance, as the chucks move up and down within their respective bowls, some of the chuck coating may flake off of the chuck, thus generating particulates and contaminants inside the bowl and the SRD module. In some cases, these contaminants may react with the residual chemicals (e.g., HF, NH3OH, etc.) present in the SRD module from previous brush scrubbing operations. It is believed that these chemical reactions between the residual chemicals and the generated particulates and contaminants of the chuck may cause the recontamination of the wafer as well as the SRD module.
In view of the foregoing, a need therefore exists in the art for a chuck assembly that improves the spin, rinse, and dry operations while providing higher reliability.